Anchoring screw for a relay strip or suture

ABSTRACT

The invention concerns an anchoring screw ( 1 ) in a bone tunnel ( 6 ) for a relay strip ( 8 ) made of synthetic material or a suture, comprising: a cylindrical proximal portion ( 3 ) of length ranging between 0 and 10 mm and a conical intermediate portion ( 4 ), whereon are provided a blunted thread ( 2 ) with a large pitch, the intermediate portion having a convergent section in the direction of, a smooth cylindrical distal portion at the rounded end and foam whereof the diameter is not less than the diameter of the bone tunnel ( 6 ).

The present invention relates to an orthopedic screw for fixing aligament graft into a bone tunnel.

All the sports that involve twisting and turning such as rugby,football, skiing, etc. place great strain on the ligaments of the kneeand therefore are in great danger of causing traumatic lesion. Thisdanger is all the worse when these sports are practiced at a high level.

The short and thick anterior cruciate ligament runs obliquely from theprespinal surface of the upper face of the tibia to the axial face ofthe external condyle of the femur and provides the knee with rotaryanterior stability.

Accidental tearing of the anterior cruciate ligament is one of thelesions most often encountered in sports injuries of the knee, oftenpartially or fully incapacitating the casualty in terms of his or herchosen sport.

Nonetheless, there are surgical techniques for reconstructing theanterior cruciate ligament that allow the stability of the knee to berestored, thus restoring its functional capabilities.

An anterior cruciate ligament may be reconstructed by means of aligament graft introduced into tibial and femoral bone tunnels, thearticular orifices of which coincide with the zones of insertion of thenatural anterior cruciate ligament.

Definitive anchoring of the graft is achieved by progressive adhesionand incorporation of the graft into the walls of the bone tunnel.

This incorporation occurs relatively quickly (in about six to eightweeks) if use is made of a graft taken from the ligamentum patellaecomprising, at each of its ends, a small bony lump originating from thepatella and from the tibia. This graft of the bone-tendon-bone type thuscomprises a ligament central part and two bony parts, the latterallowing very good attachment into the bone tunnel.

This type of excision presents not insignificant potentialdisadvantages, namely weakening of the extensor system, residual pain, arisk of fracturing the patella or of tearing the ligamentum patellae,both of which are weakened by the excision to which they have beensubjected.

In order to avoid these disadvantages, recourse may be had to ligamentgrafts taken from the tendons of the pes anserinus, that is to say themeeting of the terminal tendons of the sartorius, gracilis andsemitendinosus muscles, known as a graft of the STG type.

This is actually a less invasive technique in which the risk ofundesirable effects associated with the excision are far less high.

However, the graft thus formed is made of purely tendon tissue, that isto say tissue that has no bony lumps at its ends. This, by comparisonwith the bone-tendon-bone graft, presents a technical problem ofattaching the graft to the bone tunnel.

It should be pointed out that it takes at least three months, andsometimes longer, for the inserted tendon tissue to adhere suitably tothe wall of the bone tunnel. Throughout this time, the integrity of theset-up will therefore essentially rely on the quality of the artificialfixings installed during the intervention.

If the fixings of the graft are not effective enough, the repeatedtensile forces associated with the knee regaining its mobility willcause the graft to slip gradually in the bone tunnel and lose itsinitial tension and relax into a slack state.

Various methods of attaching ligament grafts to a bone tunnel are known,each of them having, to various degrees, serious limitations.

One customary method of attachment is to introduce a screw known as aninterference screw between the ligament graft and the wall of the bonetunnel in which the graft has already been introduced.

Experimentally, it has been possible to demonstrate that the mechanicalpull-out strength of grafts of the “STG” type fixed by interferencescrews is of the order of 35-40 daN on average.

In some extreme cases, the mechanical pull-out strength may fail toexceed 20 daN.

Furthermore, the most recent experimental studies looking into thebehavior of these grafts when subjected to cyclic tensile loadings inorder to simulate what happens during re-education, show that this typeof fixing is unable effectively to neutralize the progressive slippageof the graft that occurs at each tension spike. This slippage gives riseto a progressive loss in initial tension and may even, after a fewhundred cycles, cause the graft to pull completely out of the bonetunnel.

Finally, the crushing of tendon tissue by the screw, all the morepronounced as the attachment is desired to be firm, may be very damagingto the histological evolution of the tendon tissue which runs the riskof being sheared, experiencing necrosis, and, ultimately, incorporatinginto the bone in a way which is sometimes extremely mediocre.

Another device aimed at avoiding the disadvantages of interferencescrews is to pass through the ligament loop a relay strip of syntheticfabric itself fixed onto a small metal bar (the endobutton type). Havingpassed through the entire bone tunnel along its longitudinal axis,pulling the relay strip and the ligament loop behind it, this bar pivotsand presses against the bearing cortex and thus neutralizes any possiblepulling-out of the graft.

This type of set-up makes it possible to obtain a strength which,according to the literature, does not, however, exceed 50 daN onaverage.

However, it has been clearly demonstrated that, when subjected to cyclictensile forces, the relay strip deforms and gradually undergoespermanent elongation (this being all the more pronounced if its initiallength is long) and this also leads to a progressive loss of the initialtension applied to the graft at its time of insertion.

Now, it is acknowledged that the movements of the knee during everydaylife and, as a result, during free re-education exercises, give rise tocyclic tension spikes in the cruciate ligament or in its substitute,which may be as high as 50 daN.

What that means is that allowing the patient to undertake intensive andearly re-education, which is an increasingly pressing demand frompatients who are sportsmen and -women, after the anterior cruciateligament has been reconstructed, very obviously entails risks ofdamaging the mechanical properties of the graft namely of causing arelapse into the slack state or a risk of accidental tearing out.

These risks of damage to the fixing to a bone tunnel, which are alreadyvery real in the case of the use of a graft of the “bone-tendon-bone”type, are even greater when using a graft of the “SGT” type even thoughthe latter is far more advantageous from the point of view of thesecondary disadvantages associated with the excision.

An object of the invention is therefore to propose a device for fixing aligament graft into a bone tunnel which has good resistance to tensionin order to limit the risks of the ligament graft being pulled out of orslipping in a bone tunnel.

To this end, the invention relates to an anchoring screw for anchoring arelay strip made of synthetic material or a suture in a bone tunnel,having:

-   -   a cylindrical proximal part with a length of between 0 and 10        mm, and a conically tapered intermediate part, on both of which        a blunted screw thread with a long pitch is formed, the        intermediate part having a cross section that tapers towards    -   a plain cylindrical distal part with a rounded and blunt end,        the diameter of which is at least equal to the diameter of the        bone tunnel.

The screw according to the invention therefore comprises three distinctparts: a proximal part of cylindrical cross section, an intermediatepart of conically tapering cross section and finally the distal part ofcylindrical cross section the end of which is rounded and blunt. Thescrew comprises a large blunted and non-damaging screw thread runningexclusively along the proximal and intermediate parts.

This configuration allows this screw to perform optimally its role ofimmobilizing a textile relay strip against the wall of the bone tunnelin which a helical screw thread will have been made in advance using atap.

The textile relay strips are then passed through the bone tunnel,pulling the ligament loop along behind them. Once the graft is in place,the screw is introduced between the two strands of the relay strip andimmobilizes it by pressing it firmly against the threads in the bonewithout the risk of damaging the relay strip thanks to the rounded andblunt shape of the screw thread.

The relay strip, because of its flexibility, can deform and closely hugthe crenellated relief of the helical screw thread formed in the wall ofthe bone tunnel.

The conically tapering shape of the screw will give rise to an effect ofcrushing the relay strip against the bone wall to an extent thatincreases with the depth to which the screw is introduced.

The taper of the screw is maintained, however, only over itsintermediate part. This is because a screw that was tapered along itsentire length would carry the risk of giving rise to a wedge effectlikely to cause the bone to split open as it progressed into the bonetunnel.

The distal part of the screw, which is cylindrical and has a roundedend, corresponds to the region of transition between the fixed part ofthe relay strip fixed by the thread of the screw against the screwthread in the bone, and the free part thereof that passes through theligament loop. It is in this region that the back and forthmicromovements of the tape against the bone occur during the cyclictension-release cycles induced in the graft as the knee moves. This iswhy this distal region is entirely plain and smooth and devoid of screwthread so as to prevent any risk of the relay strip being sheared duringthe back and forth micromovements against the bone wall.

According to a preferred embodiment of the screw, the pitch, between twoconsecutive threads is equal to approximately 5 mm, which corresponds tothe space needed for the suspension relay to be able to deform freelyand closely hug the crenellations of bone created by the tap.

According to a preferred possibility, the cylindrical distal part has alength of more or less 5 to 6 mm. This distance is needed to neutralizethe back and forth micromovements of the tape against the bone duringcyclic tensions on the graft and thus avoid the risks of shearing thatwould definitely occur if the screw thread extended as far as the distalend of the screw.

In order to fit the screw, the proximal face thereof has a hexagonsocket.

As a preference, the screw thread has a thread depth of between 1 and 3mm, and preferably of 1.5 mm, so as both to fix the screw into the bonetunnel and to immobilize the relay strip.

For a clear understanding thereof, the invention is described withreference to the drawing which, by way of nonlimiting example, depictsone embodiment of the screw according to this invention.

FIG. 1 is an external view of the screw.

FIG. 2 depicts the screw in place in the bone tunnel and retaining aligament graft.

FIG. 3 depicts the proximal face of the screw.

FIGS. 4 to 9 depict the various steps in the method of reconstructing ananterior cruciate ligament using the screw that is the subject of theinvention.

FIGS. 10 to 13 depict the steps of constructing a graft to besubstituted for the anterior cruciate ligament.

FIGS. 14 to 17 depict another embodiment of the screw.

FIGS. 18 to 21 depict another embodiment of the screw.

As can be seen in the drawing, the screw 1 has a cylindro-conicaloverall shape with a helical screw thread 2. It is made of metal, forexample of titanium or of stainless steel. It may equally be made of abiodegradable material, such as a lactic acid copolymer.

The screw has three distinct parts: a proximal part 3 of cylindricalsection, about 10 mm long, an intermediate part 4 of conically taperingcross section, also about 10 mm long, and finally a distal part 5 ofcylindrical shape with a rounded and blunt end, measuring about 5 mm inlength.

The screw thread 2 extends over the proximal and intermediate part ofthe screw, and not over its distal part.

This screw thread 2, as shown by the figures, is blunted and has a longpitch. In the example depicted, the pitch, which separates twoconsecutive threads, is about 5 mm. It will also be noted that the screwthread 2 is very deep, the depth being between 1 mm and 3 mm, andpreferably 1.5 mm.

In practice, this screw is used as follows.

The intervention begins with the excision of a ligament from thesemitendinosus using conventional instruments (stripper) and the graft12 is left to one side.

Next, under endoscopic control, a graft insertion tunnel 6 is madethrough the tibia. This phase of the intervention is depicted in FIG. 4.In a way that is entirely conventional, a guide pin, the end of whichreaches the tibial point of insertion of the anterior cruciate ligamentis introduced through the bone. Conventional monitors available on themarket may be used for this. A 4.5 mm cannulated drill bit introducedfrom outside inwards, guided by the pin producing the tibial tunnel. Thelength of the tunnel is then measured.

In the same way, arthroscopy is used to select the point of attachmentof the graft to the femur and, at this point, a guide pin is introducedfrom the inside of the knee outwards. This introduction of this pin maybe performed either via the tibial tunnel (possibly adjusting the axisof penetration by varying the degree of flexion of the tibia) or via theantero-internal arthroscopic approach.

It is also possible, by using a monitor intended for that, to introducethe pin from outside inwards, according to the operating surgeon'spreferences.

Like with the tibia, a tunnel approximately 4.5 mm in diameter is thenmade using the same hollow drill bit sliding along the femoral guidepin. The length of the femoral tunnel L1 and the distance separating thetwo, femoral and tibial, intra-articular orifices L2 (theintra-articular length of the graft) are measured.

The most appropriate length of fixing screw and the depth of bonehousings to be produced in order to accommodate the graft can then beselected according to the length of the bone tunnels. The maximum lengthof the graft will need to correspond to the sum of the depth of the twohousings (femoral and tibial) and the intra-articular length L2.

The graft can then be prepared to the dimensions thus measured.

One way of preparing the graft 12 is to excise a tendon, preferably thesemitendinosus. The two ends of the graft 12 are then attached to oneanother to form a closed loop (the size of which is twice the desiredsize of the final graft) as shown in FIG. 10. The graft is then twistedon itself into a figure-of-eight shape (see FIG. 11) then folded ontoitself to obtain a four-strand closed loop comprising a single suture,the graft 12 in this configuration is depicted in FIG. 12.

Another way of preparing the graft is to wind it around two pivotmarkers the separation of which corresponds to the final dimension ofthe graft. One or two ligatures produced at each end of the graftprovide a very easy and effective way of neutralizing any possibleslippage of the strands of ligament with respect to one another and agraft 12 which is extremely strong in tension is thus very soonobtained.

Each end of the graft 12 is calibrated with a view to determining thediameter of bone housings to be produced.

Two relay tension strips 8, each 40 or 50 cm long, are slipped throughthe ligament graft and wrap around each tension pole thereof, asdepicted in FIG. 13. The relay strips 8 may be made of a syntheticmaterial such as a polyester terephthalate. One example of this materialused in surgery is Mersilene. The relay strips 8 are about 7 mm wide.

The strips 8 are fixed to the pulling posts of a stretcher the spring ofwhich is calibrated to exert continuous tension of about 40 daN. Thistension will be exerted on the graft 12 throughout the preparation ofthe bone tunnels so as to neutralize any plastic deformation of thegraft and of the textile material of which the relay strips 8 are madewhich could occur gradually as the system is being tensioned.

The tibial and femoral bone housings are then prepared, with thediameter and depth determined previously.

In the femur, the housing may be produced in the conventional way usinga graduated and cannulated auger introduced via the antero-internalarthroscopic approach and guided along a guide pin introduced into thefemoral tunnel via the same approach.

This housing could equally be produced using a special auger introducedvia the tibial tunnel, as can be seen in FIG. 6.

This instrument consists of a hollow tube with a diameter slightlysmaller than 4.5 mm, equipped at its end with a fine cutter in the shapeof a wing. A guide pin 16 introduced into the tibial tunnel allows theauger, which is tapped in with a hammer from outside the tibia towardsthe articular cavity, to be guided. The cutter 17 of the auger creates,in the bone through which it passes, a small intra-osseous groove oflittle significance until it reaches the actual site of the articularcavity, where the instrument can then turn freely and create a housing7, either a femoral housing (by moving forwards) or tibial housing (bymoving backwards), the diameter of which corresponds to twice the radiusof the auger and of its cutter 17.

It is also possible to conceive of boring out the tibial housing 7 usingan auger composed of a fine handle and of an end corresponding to thedesired diameter for the tibial housing. This auger would be introducedvia the antero-internal approach, the fine handle sliding along a guidepin placed in the femoral tunnel. Once the auger had been completelyintroduced into the knee, by varying the degree of flexion, the axis ofthe tibial and femoral tunnels could once again be made to coincide sothat the guide pin could be introduced into the tibial tunnel frominside the knee and the housing then produced simply by turning theauger on this pin inside the tibia until the desired depth was reached.Another possibility could consist in introducing a fine handle into thetibial tunnel from the outside inwards, then, via the antero-internalapproach, introducing a cutting instrument of the desired diameterdesigned to be articulated with the tibial handle which would then alsoactuate the cutting part backwards.

The preparation of the bone tunnels 6 ends with the introduction of atap 18 intended to prepare a screw thread 19 for the fixing screw. Thisoperation is depicted in FIG. 7.

This tap is introduced into the femur from outside inwards through ashort incision in the skin measuring 1 to 2 cm. Its direction isdictated by the guide pin introduced into the femoral tunnel 6.

In the same way, the tap 18 is introduced into the tibia from theoutside inwards and also slides along the guide pin.

The tension strips 8 for pulling the graft 12 are introduced via theantero-internal approach, pulled into the femoral and tibial bonetunnels 6 by means of a simple pulling filament in the form of a lassoand then recovered on the outside of the knee, as can be seen in FIG. 8.

A fine metal filament running through the proximal pole of the graft andemerging between the two pulling strips is passed through the femoraltunnel at the same time as the strips. The other end of the filamentemerges via the antero-internal approach.

This metal filament will allow the fixing screw 1 to be guided as far asthe entrance to the bone tunnel without a surgical approach having to bemade in the femur.

The graft 12 is pulled into the femoral housing simply by pulling on therelay strips 8. The screw 1 is then introduced into the tunnel 6 whereit is guided by the metal filament. As soon as the screw finds itshousing, the filament can be removed simply by pulling it.

The pulling of the strips 8, on the tibia side, completes theintroduction of the graft into the tibial housing 7.

The position and the tension of the graft 12 are checked endoscopicallyprior to the final locking operation which is carried out using thetibia screw 1.

If the tension is not satisfactory, the tibia screw 1 can be withdrawn,tensioning resumed, and locking obtained once again by fully introducingthe screw 1. The relay strips 8 are then cut off flush with the screw 1.That is performed under the control of the view at the tibia and bymeans of an instrument of the guillotine type at the femur.

FIG. 2 shows the ligament graft 12 in place in the bone housing 7 andsuspended by the synthetic relay 8 pressed firmly by the screw 1 againstthe screw thread formed in the wall of the bone tunnel. It can be seenthat the graft is fixed partially in the cortex region 9 and partiallyin the spongy region 10 of the bone.

The invention thus provides an anchoring screw for anchoring a ligamentgraft in a bone tunnel that has the numerous advantages mentioned above.

First of all because of the pulley effect created by the use of aligament graft in a closed loop with four strands: the tensile forceintroduced into the graft will be quartered at the suture.

Secondly, as the synthetic relay strips 8 pass freely through theligament loop, the tensioning of these strips will allow the force to beautomatically distributed equally through each of the strands that makeup the graft.

Thirdly, the use of relay strips 8 makes it possible to obtain a firmattachment while at the same time avoiding the risk of damaging theligament tissue by crushing it forcibly against the wall of the tunnel.

Fourthly, the tensile strength afforded by a flexible relay strip 8fixed by interference screws is far greater than that obtained by thetraditional methods. Tests carried out in a mechanical laboratory haveshown that the pull-out strength of a 7 mm Mersilene tape fixed intohuman bone using a screw according to the invention varied with thespecimens (according to the bone quality) between 120 and 220 daN,namely three or four times higher than the strength obtained withconventional interference screws. This strength greatly exceeds, andthis is true for all individuals, the 50 daN peaks of tension that thegraft will have to withstand during free re-education exercises. Cyclictensile testing evaluating means of attachment of ligament graftscommonly used (interference screws, stirrup pieces, etc.) have shownthat during tests at 45 daN, the best specimens were unable to withstandmore than 200 to 300 cycles. By contrast, with a 7 mm Mersilene stripheld by the screw that is the subject of the invention, cyclic tensiletests comprising rounds of 600 tension cycles varying from 2.5 to 25 daNalternating with rounds of 600 tensile cycles varying from 5 to 50 daNdemonstrated that, after 33 800 cycles, the specimens showed noperceivable sign of degradation of their mechanical properties(rigidity, pull-out strength).

A fifth advantage of the use of relay strips 8 is a saving on the amountof tendon tissue that has to be excised to form the graft, because thefixing is performed by means of synthetic tissue rather than by means ofthe tendon itself as was the case in the traditional techniques. Thatmeans that the tissue removed is shorter, and therefore causes markedlyless trauma.

It goes without saying that the invention is not restricted to theembodiment described hereinabove by way of nonlimiting example but that,on the contrary, it encompasses all embodiment variants thereof. Thescrew may, for example, exist with other sizes so as to meet themechanical and physiological requirements of particular cases.

Thus, it would also be possible to anticipate using the screw accordingto the invention for fixing not a synthetic strip but sutures into abone, for the attachment of soft tissue.

This use of the screw is illustrated in FIGS. 14 to 17. In this use, ablind hole 20 is pierced in a bone, a screw thread 21 is then made inthe wall of this hole. A suture 24 is pushed into the bottom of the hole20, the suture 21 is then locked in place by a screw 1 according to theinvention. This use of the screw makes it possible to avoid the use offixing anchors, one example of which is illustrated by document WO95/15726.

The disadvantages of these anchors are, on the one hand, that they areexpensive and, on the other hand, that when one of the sutures breaks,the entire anchor has to be replaced.

In this embodiment, the screw of course has suitable dimensionsgenerally very much smaller than those of the screw used in the case ofthe reconstruction of a knee.

Another possible embodiment of the screw is depicted in FIGS. 18 to 21in the case of desinsertion of a ligament.

FIG. 18 depicts a case of desinsertion of a ligament, that is to say thetearing of the point of attachment of a ligament 25 to a bone.

A tunnel 26 through the bone is made at the point of ligamentdesinsertion and a housing 27 for the screw is prepared percutaneously.

A lacing of sutures 28 is performed in the end of the ligament 25 thatis to be reinserted, as can be seen in FIG. 19.

The sutures 28 are then passed through the bone tunnel then recoveredthrough a miniscule incision in the skin.

Pulling of the sutures 28 re-tensions the ligament 25 at the entry tothe bone tunnel 26 as can be seen in FIG. 20.

The screw 1 is then introduced percutaneously and locks the sutures 28(see FIG. 21).

This use of the screw is therefore not very invasive and eliminates theneed to produce attachment knots something which, in practice, may provetechnically difficult and dictate a surgical approach on the externalface of the bone.

It should be noted that in the case of short tunnels in bone, thecylindrical part of the screw may be shortened or non-existent, that isto say of zero length. In this case, the taper of the intermediate partmay be accentuated and the distal part may also have its length reduced.

1. A method for fixing a ligament graft into a bone tunnel, the methodcomprising: making a graft insertion tunnel in a tibia and in a femurand making a helical screw thread in each of the tunnels; preparing aligament graft having a plurality of poles to an appropriate dimensionand forming a multiple strands closed loop; slipping at least one relaytension strip through each of the poles of the graft; passing one of therelay strips through the tunnel in the tibia and another of the relaystrips through the tunnel in the femur and pulling the graft alongbehind the relay strips; and introducing a screw between two strands ofeach relay strip and immobilizing each one of the relay strips bypressing the screw against a respective one of the helical screw threadsin each of the tunnels made in a bone, the screw comprising: acylindrical proximal part with a length of between 0 and 10 mm; aconically tapered intermediate part; and a blunted screw thread with along pitch formed on both the cylindrical proximal part and the taperedintermediate part; wherein the tapered intermediate part has a crosssection that tapers towards a plain cylindrical distal part with arounded and blunt end, a diameter of the cylindrical distal part is atleast equal to a diameter of a bone tunnel.
 2. The method as claimed inclaim 1, wherein the method of preparing the ligament graft comprises:excising a ligament from the semitendinosus to obtain the graft;attaching two ends of the graft to one another to form a closed loop;twisting the closed loop on itself into a figure-of-eight shape; andfolding the shape onto itself to obtain a four-strand closed loopcomprising a single suture.
 3. The method as claimed in claim 1, whereinprior to the insertion of the graft through the bone tunnels, the relaystrips are fixed to pulling posts of a stretcher, the stretcher having aspring calibrated to exert continuous tension of about 40 daN.
 4. Themethod as claimed in claim 1, further comprising preparing a bonehousing in the tibia and in the femur for receiving each one of an endof the graft, each bone housing being calibrated according to thepreviously measured diameter of each graft's end.
 5. The method asclaimed in claim 4, wherein the femoral or the tibial housing isproduced using an auger equipped with a cutter, the auger beingintroduced via a femoral or tibial tunnel from outside towards thearticular cavity and creating a small intra-osseous groove when guidedin the femoral or tibial tunnel before reaching an actual site of anarticular cavity, where the auger can then turn freely and create ahousing into the bone by moving forwards or backwards.
 6. The method asclaimed in claim 1, wherein the method of making the helical screwthread in the femur or in the tibia comprises introducing a tap into thefemur or the tibia from outside inwards through a short incision in askin, the tap direction being dictated by a guide pin introduced intothe femoral tunnel.
 7. The method as claimed in claim 1, wherein themethod of preparing the ligament graft comprises: excising a ligamentfrom the semitendinosus to obtain the graft; winding the ligament aroundtwo pivot markers separated from one another by a distance equal to thefinal dimension of the graft; and providing one or more ligatures ateach end of the graft.